1. Field of the Invention
The present invention relates to an optical pickup apparatus which detects reflected light from an optical recording medium. The present invention also relates to an optical disk apparatus having the optical pickup apparatus. The present invention also relates to a tracking error signal detection method of detecting a tracking error signal on the basis of the reflected light detected by the optical pickup apparatus.
2. Description of the Related Art
A push-pull method (PP) is known as a tracking scheme of an optical disk. In PP, since the symmetry shifts due to movement of the objective lens in the tracking direction, an offset is generated. To suppress this offset, the offset amount is electrically canceled while monitoring the moving amount of the objective lens in the tracking direction. A differential push-pull method (DPP) using three beams is also known. Alternatively, a method of driving a hologram integrally with the objective lens is also known.
When the method of monitoring the moving amount of the objective lens in the tracking direction is applied, a position sensor which monitors the moving amount must be arranged in the optical pickup apparatus. Hence, the apparatus becomes bulky and therefore cannot be applied to a small and thin optical pickup for, e.g., a notebook PC. Additionally, the newly required position sensor increases the cost of apparatus.
DPP is a scheme of canceling an offset using three beams. About 80% of laser output light account for a main beam, and about 20% account for a side beam. Hence, this scheme cannot be used in an optical pickup which has no margin in laser output light, as in a recording system. The interval between the main beam and the side beam is about ½ the track pitch. For this reason, this scheme cannot be used in an optical pickup which records on media such as a DVD-RAM and DVD-R having different track pitches.
The method of driving the hologram integrally with the objective lens can effectively be used for a disk such as a DVD-RAM having a high PP signal modulation ratio for a light receiving signal. However, for a disk such as a DVD-R having a low PP signal modulation ratio for a light receiving signal, the Gaussian distribution of the beam on the aperture has a deviation due to a shift of the objective lens, and an offset of PP signal is generated.